The use of ultraviolet detection tubes is well known in the prior art. Through use of such devices, it has been found that the ability of the tube to respond to ultraviolet is definitely affected by the temperature to which the tube is exposed. The lowered temperature slows down the rate of travel of the ions resulting from tube discharge and for situations which require a high number of discharges within a short period of time, the presence of these ionized particles has been found to cause false discharges. In practice, and that particularly related to fire detection, the false operation of such a detector has had adverse effects both from the economic and safety standpoints. In such fire detection situations, it is important that the apparatus not only properly detect a flame which is the source of the ultraviolet, but also that the apparatus not respond to ambient conditions to provide false actuations of the fire control system.
The standard operation of a detector such as the Geiger-Mueller type is that when the electrodes of the detector are impressed with a voltage of sufficient magnitude, and when ultraviolet radiation strikes the cathode, the device will pass a current between the electrodes via the ionized gases created in the discharge process. The device will continue to conduct until the impressed voltage is reduced below the point that supports the ionization process. If, however, the voltage is restored and the ultraviolet radiation source is still present, the detector will again discharge for as long as the voltage level is sufficiently high. Thus, a tube of this type, in order to provide environmental testing for the presence of ultraviolet radiation must experience alternate ionization and a de-ionization of the gases between the electrodes of the detector. Should the de-ionization process not be sufficiently complete, restoration of the impressed voltage would result in discharge of the tube without ultraviolet initiation.
In temperatures above approximately 30.degree. F., the de-ionization process can normally be accomplished by providing a short duration "off" time before restoring voltage across the electrodes. When the temperature drops, the mobility of the gases is decreased and the de-ionization process takes much longer.
The primary purpose of this invention is therefore, to decrease the de-ionization time by one of several various alternatives.
It is an object of this invention to decrease the de-ionization time of ulraviolet detection devices which devices contain an ionizable gas.
It is an object of this invention to increase the de-ionization surface of an ultraviolet detection tube after discharge thereof such that the increased surface area will decrease the time for the de-ionization of the gas within the tube.
It is a further object of this invention to control the number of ions generated in the discharge process of an ultraviolet device, which device contains an ionizable gas.
It is a further object of this invention to provide a means for shorting the electrodes of an ultraviolet detection tube for the rapid de-ionization of gases within the tube after discharge thereof.
It is yet a further object of this invention to provide a temperature responsive control circuitry for an ultraviolet detection device which will increase the time during which the electrodes of the device are below discharge voltage such that a longer time for de-ionization of the gases within the device is provided.